1. Field of the Invention
The present invention relates to deferred action batteries or seawater batteries of the type wherein the battery is immersed in seawater so that seawater filling the battery functions as the electrolyte.
2. The Description of the Prior Art
Deferred action batteries of the type using seawater as the electrolyte are commonly constructed using a plurality of spaced apart parallel silver chloride battery plates and magnesium battery plates arranged in alternately stacked relationship. Batteries of this type are described, for example, in U.S. Pat. No. 3,630,782; issued Dec. 28, 1971 to Butler, U.S. Pat. No. 3,306,775; issued Feb. 28, 1967 to Burant et al., U.S. Pat. No. 3,431,148; issued Mar. 4, 1969 to Jones, and U.S. Pat. No. 3,451,855; issued June 24, 1969 to Jones et al. Batteries of the type shown in these patents have been found to be useful in a number of applications, but due to the use of silver in their construction they tend to be expensive.
The cost of such batteries can be substantially reduced by substituting lead chloride plates for the silver chloride plates therein, thereby eliminating the material cost of the silver. Seawater batteries having such lead chloride plates are referred to, for example, in U.S. Pat. No. 3,468,710; issued Sept. 23, 1969 to Kransnow et al., in U.S. Pat. No. 3,943,004 issued to Honer et al. Mar. 9, 1976, and in U.S. Pat. Application Ser. No. 653,270; filed Jan. 28, 1976, and assigned to an assignee in common with that of the present invention.
Use of lead chloride plates as the cathode electrode in seawater batteries has, however, presented some drawbacks because the chemical reaction occuring in the battery produces quantities of solid waste precipitate which tends to clog up the battery and thereby reduce its effective life. In a lead chloride magnesium type battery, when seawater flows into the battery, an electrical potential is produced as a result of the electro-chemical reactions at the electrodes.
At the cathode EQU PbCl.sub.2 + Mg .fwdarw. MgCl.sub.2 + Pb
At the anode EQU Mg + 2H.sub.2 O .fwdarw. Mg (OH).sub.2 + H.sub.2
the magnesium hydroxide Mg(OH).sub.2 produced by the latter reaction forms a precipitate which accumulates in the battery. Unless this precipitate material is permitted to migrate out of the battery through the seawater inlet openings, it results in the clogging of the battery and premature termination of its useful life. However, the useful life of the battery would be similarly shortened if larger ports were provided to permit escape of the precipitate from the battery. Such ports would of necessity result in increased flow of seawater into the battery and consequent communication of seawater electrolyte between the cells of the battery thereby causing unnecessary ion transfer between cells and premature failure of the battery. The accumulation of magnesium hydroxide precipitate is also encountered in silver chloride-magnesium seawater batteries commonly used, but in the lead chloride batteries the problems inherent in the accumulation of precipitate are substantially increased. Compared to a silver chloride battery, a lead chloride battery employs a greater number of stacked cells to produce the same voltage since each of the stacked cells of a lead chloride battery produce about 1 volt whereas similar cells of a silver chloride battery produce approximately 11/2 volts. Therefore, if compared to a silver chloride battery, a lead chloride battery requires a greater number of cells stacked together, the battery is thicker, and consequently the precipitate must migrate greater distances if it is to be emitted from the water inlet opening. On the other hand, it is not efficient to indiscriminately increase the size or number of the water inlet openings to permit emission of the precipitate magnesium hydroxide since it is necessary to control the amount of water admitted into the battery and the intercell flow of water. Therefore, in order to maximize the efficiency and the useful life of a lead chloride seawater battery it is necessary to restrict the size of the water inlet opening yet provide means to facilitate emission of precipitate solid materials from the battery through the seawater inlet opening.